This invention relates generally to light coupling devices and fiber optic modules. More particularly, the invention relates to an optical block for coupling optical elements to small form factor fiber connectors.
Fiber optic modules interface optical fibers to electronic circuitry transducing light or photons into electrical signals or vice versa. A fiber optic module may be a fiber optic receiver, transmitter or transceiver including both receive and transmit functions. The fiber optic receiver, transmitter and transceiver each including optical elements (OE) and electrical elements (EE), including optoelectronic devices.
The fiber optic transmitter OE includes an emitter (such as a semiconductor LED or Laser) mounted in a package and an optical coupling element for coupling light or photons from the OE into the optical fiber. The type of semiconductor laser (light amplification by stimulated emission of radiation) may be a vertical cavity surface emitting laser (VCSEL).
The fiber optic receiver OE includes a photodetector (such as a photodiode) mounted in a package and an optical coupling element for coupling light or photons from the optical fiber into the photodetector. The EE for each includes integrated circuits and passive elements mounted on a substrate such as a printed circuit board (PCB) or ceramic. The OE and EE coupled together at the emitter and photodetector.
Because of the high transmission frequencies utilized in fiber optic communications, crosstalk between receive and transmit signals is of concern. In order to avoid electronic crosstalk and electro-magnetic interference (EMI), the fiber optic transceiver usually employs separate components and separate shielding of fiber optic receiver and fiber optic transmitter components. In order to avoid optical crosstalk where light or photons can interfere between communication channels, the fiber optic transceiver usually employs separate optical elements for coupling light or photons into and out of the optical fiber for fiber optic receiver and fiber optic transmitter.
The form factor or size of the fiber optic module is of concern. The trend is towards greater usage of fiber optic communication requiring improved connectivity and smaller optical fiber connectors to more densely pack them on a system printed circuit board. Additionally, the desire for tighter interconnect leads of fiber optic cables, restricts the size of the OE""s. For example, in the common implementation using a TO header and can, the header dimension of the interconnect lead is normally 5.6 millimeters (mm). In small form factor optical modules, such as the MT family, the two optical fibers are separated by a distance of only 0.75 mm. This severely restricts the method of coupling light or photons from the OE into and out of fiber optic cables.